The present invention relates to a voltage regulator, and more specifically relates to a voltage regulator of the voltage boosting/lowering type comprised in the combination of a switching regulator block and a series regulator block.
FIG. 2 is a block diagram of the conventional voltage regulator. The regulator is comprised of a switching regulator block 111 and a series regulator block 110. The preceding switching regulator block 111 receives an input voltage V.sub.IN at its input terminal 101 and produces a boosted intermediate voltage V.sub.SW of a constant level at its junction terminal 102. The succeeding series regulator block 110 receives the intermediate voltage and produces a lowered output voltage V.sub.OUT of a constant level at its output terminal 108.
However, the conventional regulator has the following drawbacks. A level of the intermediate voltage V.sub.SW at the junction terminal 102 is determined by a resistance ratio of internal voltage-dividing resistors connected to the junction terminal 102. On the other hand, a level of the output voltage V.sub.OUT at the output terminal 108 is determined by another resistance ratio of internal voltage-dividing resistors connected to the output terminal 108. Namely, the intermediate voltage V.sub.SW at the junction terminal 102 and the output voltage V.sub.OUT at the output terminal 108 are determined independently from each other. Therefore, the series regulator block 110 has a voltage conversion efficiency determined by V.sub.OUT /V.sub.SW which is held constant regardless of an amount of an electric current taken from the output terminal 108, thereby hindering the operative efficiency of the voltage regulator.